In arrangements of wind turbines in a wind turbine park, oftentimes wind flow conditions for individual wind turbines do not differ significantly. This is particularly true for offshore wind turbine parks, where typically turbulence is very low. Consequently, differences in rotor rotational speed between individual wind turbines are low, and, at the same time, the rotor rotational speed of each individual wind turbine is relatively constant.
For controlling the rotor rotational speed of a wind turbine, two main approaches are known in the art. The first is braking, either with electrical or mechanical means. The second is to modify the blade pitch, that is, to increase or decrease the angle of attack, i.e. the angle at which the wind strikes the rotor blades. This is typically performed with actors on a hydraulic or electric basis.
In spite of relatively uniform wind flow conditions and the means for rotation control known in the art, parks of horizontal-axis wind turbines require a significant amount of measurement and data processing for applications that are dependent on the azimuth angles of the wind turbines, with the azimuth angle being the angle of rotation of the rotor around the axis perpendicular to the plane of the rotor blades. For each such application, each individual azimuth angle is measured and subject to calculations specific to the application, which can in turn lead to a significant computational load and a relatively high control complexity.
WO 01/97359 A1 describes a method and device for stabilising power generated by groups of generators wind turbines. The method and the device generally aim to offset the phase angles of rotating rotors of wind turbines, or groups of wind turbines, relative to each other. In case wind turbines of a wind park are grouped into different groups of wind turbines the wind turbines of a group may be synchronized. However, phase shifts are introduced between the groups of wind turbines of a wind farm in order to avoid occurrence of so called singularity phase angles of different groups of wind turbines at the same time.
DE 101 64 524 A1 and WO 2007/068254 A1 describe warning lights at the blade tips of a wind turbine rotor.
EP 1 835 293 A1 describes a method of determining at least one rotation parameter of a wind turbine rotor on the bases of variations in measured effective centrifugal forces due to gravitational influence.
The article “Obstacle Markings on Wind Turbines for Save Aviation and Marine Navigation” by Björn Montgomerie, FOI memorandum, Swedish Defense Research Agency SE, number 979 (Aug. 1, 2008) pages 1 to 10 describes illumination of a wind turbine at the highest point. Lights are provided at blade tips which undergo and on/off circle.